1. Field of the Invention
The present invention relates generally systems, methods and compositions for loading and detonating industrial explosives in a borehole and more specifically to systems, methods and compositions for loading and detonating explosives in the form of water gels, slurries and emulsions in boreholes where the boreholes have been formed in rock formations that are at elevated temperatures at or above the allowable exposure temperature for using such explosives in underground mining applications.
2. Description of the Related Art
The use of explosive compositions, including but not limited to water gels, slurries and emulsion-type explosives, in various types of blasting operations, including underground mining, has dramatically increased in recent years because of the economy and excellent explosive characteristics of such compositions. The advent of modern technologies in manufacture of explosives including emulsions has led to site-mixed slurry explosives. As the name suggests, such site-mixed slurry explosives are manufactured on site in a specially designed pump truck by carrying non-explosive ingredients in separate chambers, mixing them in specific proportions and pumping them in liquid form directly in to boreholes. The pumped mixture acquires the characteristics of an explosive within about ten minutes of pumping and solidifies slowly to the shape of the borehole. Unlike bulk emulsions, the site mixed slurry can be pumped in various densities ranging from 0.6 g/cm3 to as high as 1.20 g/cm3 and the energy can be varied to produce different types of chemically balanced explosive products to suit the rock conditions.
The slurry explosive generally has a high viscosity so that the slurry will not flow out of the borehole, fissures or joint gaps in the rock both during loading and thereafter prior to detonation. To be able to pump such high viscosity slurry explosives from the mix truck to the borehole, it is often necessary lubricate the interior of the loading pipe. For example, U.S. Pat. No. 4,273,147, the entirety of which is incorporated by this reference, a water film or water to which ammonium nitrate has been added is used to lubricate the loading pipe in order to allow the slurry explosive to be pumped through the loading pipe while maintaining safe pump pressures.
Any of the various known slurry explosives may be used in accordance with the present invention, including water-in-oil emulsions that are well known in the art. U.S. Pat. No. 4,931,110, the entirety of which is incorporated by this reference, discloses such an emulsive-type explosive material. Emulsive-type explosives usually contain an emulsifier such as a bis-alkanolamine or bis-polyol derivative of a bis-carboxylated or anhydride derivatized olefinic or vinyl addition polymer. Such emulsifiers impart improved stability and detonation properties to the explosive. Some emulsion-type explosives comprise a water-in-oil emulsion wherein the oil phase is a hydrocarbon fuel component and the dispersed aqueous phase is an aqueous solution of inorganic oxidizing salts. Various other materials, including sensitizing agents and additional fuels for example, can be employed in a variety of different formulations. Typical water-in-oil emulsion explosive compositions are set forth in detail in U.S. Pat. No. 3,447 to Bluhm, the entirety of which is incorporated by this reference.
ANFO (Ammonium Nitrate-Fuel Oil) explosives are a common water-in-oil type explosive in which ammonium nitrate, being oxygen positive, is often used as oxygen supplier in addition to being an explosive base. Such ANFO explosives have a density of between about 1.07 to 1.1 g/cc. Depending on the mixture, some ANFO explosives have good water resistance (e.g. Emulsion/ANFO 100/0, 70/30, 60/40, 40/60, 35/65), while others have poor water resistance (e.g., Emulsion/ANFO 25/75, 20/80, 10/90). The temperature ranges of use for ANFO explosives ranges from about −4 degrees Fahrenheit to about 122 degrees Fahrenheit.
It is also the case that explosive producers have begun using gassed slurries. These gassed slurries may be mixed with micro balloons or other porous additives. Likewise, gassed slurries may be formed by chemically gassing the slurry by adding a gassing agent to the slurry mix prior to being pumped to the borehole location or by adding a gassing agent at the end of the loading pipe just before entering the borehole.
Since pumping emulsion explosives involves the input of dynamic or kinetic energy into the explosive, attendant safety concerns are present. In addition to the potentially high operating pressure required for the pump, a pump running against a dead head can add considerable energy to the emulsion explosive being pumped, and could result in an unwanted detonation. In addition, if the pump is run “dry” such that no emulsion explosive is being pumped, any residual product also may experience considerable energy input to the extent that it may overheat and self-detonate. Thus, sophisticated pump monitoring and shut-down systems have been designed and implemented in various emulsion explosives pumping applications.
To address some of these concerns, various systems have been developed whereby emulsion explosives can be extruded pneumatically at a relatively low pressure from a pressurized vessel through an outlet and delivery hose. The addition of a water injection system provides an annular stream of water around the extruded emulsion explosive to lubricate its passage through the delivery hose. The use of a water injection system in the delivery of an emulsion explosive through a delivery hose is set forth in U.S. Pat. Nos. 4,273,147 and 4,615,752, the entirety of each of which is incorporated by this reference. Such water injection systems help reduce the pumping pressure requirements of a pump system, provided the water annulus is maintained. The combination of a pneumatically operated pressurized vessel for extruding the emulsion explosive and a water injection system for lubricating the flow of the emulsion is set forth in U.S. Pat. No. 5,686,685, the entirety of which is incorporated by this reference.
The use and the conditions for such use of all slurry explosives in the United States are federally regulated. 30 CFR §57.6905 sets forth the requirements for protecting such explosive material from extreme temperatures. Specifically, Section 57.6905(a) states, “Explosive material shall be protected from temperatures in excess of 150 degrees Fahrenheit.” This temperature threshold was based upon the 1992 Bureau of Mines Information Circular No. 9335, Blasting Hazards of Gold Mining in Sulfide-Bearing Ore Bodies; MSHA's Investigation Report No. D7431-S949, Investigation of Premature Detonations, Paradise Peak Mine, (Dec. 10, 1991); and the IME Safety Library Publication No. 4, “Warnings and Instructions for Consumers in Transporting, Storing, Handling and Using Explosive Materials,” (March 1992), all of which suggest a hazardous change in stability of explosives once temperatures reach this level.
Thus, whether or not a specific explosive material is capable of use in conditions that are above 150 degrees Fahrenheit, Federal regulations prohibit such use. Moreover, some explosives, such as certain ANFO explosives may be rated for use at temperatures below 150 degrees Fahrenheit. Thus, the user of such explosives not only needs to be certain that conditions of use of such explosives does not exceed federal guidelines, but that such conditions do not exceed the limits of the product as well.
The causes of elevated temperatures in underground mining can be due to geothermal heating (e.g., volcanic activity), geothermal gradients, burning coal seams, and sulphide oxidation that creates reactive ground conditions. In deep mining, rock face temperatures increase with the depth of the mine. Typically, the rock face temperature will increase at least one degree Celsius for every 100 meters of depth.
Because of the depth required to reach certain precious metal deposits, for example, the rock face temperatures can be at or above the allowed temperature limits of explosive materials. For example, platinum is exceedingly difficult to mine and extract and rock face temperatures can be well above the 150 degree Fahrenheit limit usually allowed for use of explosives. In Northam Platinum's Zondereinde mine in South Africa, rock face temperatures get as high as 162 degrees Fahrenheit and its shafts extend as far as 1.4 miles below the Earth's surface.
In addition, rock face environments may contain sulphides that through oxidation can form a reactive ground condition in which the explosive material can inadvertently detonate. The term “reactive ground” refers to rock that undergoes a spontaneous exothermic reaction after it comes into contact with nitrates. Such reactions involve the chemical oxidation of sulphides (usually of iron or copper) by nitrates. The resulting reaction can cause the liberation of potentially large amounts of heat. Thus, even in conditions where rock face temperatures are believed to be below the threshold temperature limit for explosives, chemical reactions within the formation can cause localized hot spots within the formation that exceed the allowable temperature. Because of the unpredictable nature of such chemical reactions, dangerous conditions may exist without being detected and can results in premature detonation of explosives.
Thus, there exists a need in the art to provide devices, compositions and methods for using such devices and compositions that allow use of explosives in underground mining where rock face temperatures are at or exceed 150 degrees Fahrenheit. There also exists a need in the art to provide devices, compositions and methods for using such devices and compositions that allow use of explosives in underground mining where reactive ground conditions exist. There further exists a need in the art to provide devices, compositions and methods for using such devices and compositions that are easy to use with existing explosives equipment that is easy and safe to use in underground mining where rock face temperatures are at or above 150 degrees Fahrenheit and/or where reactive ground conditions exist.